1. Field of the Invention
The present invention relates to a reflecting mirror support apparatus for supporting a reflecting mirror used for an infrared or optical telescope.
2. Prior Art
FIGS. 15(a) and 15(b) are sectional views showing the prior art reflecting mirror support apparatus.
In the drawing, the numeral 101 denotes a thick reflecting mirror; 102 a mirror cell for supporting the thick reflecting mirror (supporting means); 103 an axial force supporting mechanism for supporting thick reflecting mirror 101 which mainly consists of counter weight 130a and link 130b and supports the thick reflecting mirror 101 without distorting the surface thereof. The numeral 104 denotes a lateral force supporting mechanism mainly consisting of counter weight 104a and link 104b, which also supports the thick reflecting mirror 101 without distorting the surface thereof. The numeral 105 denotes a reflecting mirror supporting part mainly consisting of a thin rod for supporting the thick reflecting mirror 101 at a predetermined position on the mirror cell 102. The numeral 106 denotes the center of the rotation axis (not indicated in the drawing) for changing the elevation angle of the thick reflecting mirror 101 by 0.degree.-90.degree..
Next, an operation of the prior art reflecting mirror support mechanism will be explained.
When the thick reflecting mirror 101 is employed to observe stars, etc., the mirror cell 102 changes the elevation angle of the thick reflecting mirror 101 by 0.degree.-90.degree.. In that event, load almost as heavy as self-weight of the thick reflecting mirror 101 is applied on the mirror in the direction opposite to the self-weight in order to prevent the surface of the thick reflecting mirror 101 from being distorted due to the change in elevation angle, whereby deformation of the thick reflecting mirror is prevented. The axial force supporting mechanism 103 applies a force on the thick reflecting mirror 101 in the axial direction (axis of the mirror), whereas the lateral force supporting mechanism 104 applies a force on the thick reflecting mirror 101 in the lateral direction (direction perpendicular to the mirror axis).
The reflecting mirror supporting part 105 supports the thick reflecting mirror 101 at a predetermined position on the mirror cell 102. One end of the supporting part 105 is affixed to the bottom surface of the thick reflecting mirror 101 by adhesives, etc. with the other end being coupled to the mirror cell 102.
Since the thick reflecting mirror 101 and mirror cell 102 differ in coefficient of thermal expansion, relative displacement occurs between them as the ambient temperature changes. Furthermore, as the mirror cell 102 transforms with the change in elevation angle, relative displacement occurs between the thick reflecting mirror 101 and mirror cell 102 as the elevation angle of the mirror cell 102 changes.
However, the reflecting mirror supporting mechanism 105 consisting of a thin rod has a low rigidity except in the direction of the axis of the mirror. Therefore, the aforementioned relative displacement is absorbed by deformation of the thin rod comprising the supporting mechanism 105.
Although moment is generated on the thick reflecting mirror 101 by deformation of the reflecting mirror supporting mechanism 105, it does not cause substantial (detrimental) deformation of the thick reflecting mirror 101 because the mirror 101 has a high rigidity.
When an external force such as wind acts on the surface of the thick reflecting mirror 101, such a force is transferred to the mirror cell 102 via reflecting mirror supporting mechanism 105.
The axial force supporting mechanism 103 balances the weight of the thick reflecting mirror 101 and counter weight 103a, whereby it is possible to support the weight of axial components of the thick reflecting mirror 101 irrespective of the elevation angle of the thick reflecting mirror 101. Furthermore, even though the thick reflecting mirror 101 and mirror cell 102 expand and contract in response to differences in coefficient of thermal expansion, etc., the link 103b prevents an excessive force from being applied directly on the thick reflecting mirror 101.
Likewise, the lateral force supporting mechanism 104 balances the weight of the thick reflecting mirror 101 and counter weight 104a, whereby it is possible to support the components of weight in the radial direction of the thick reflecting mirror 101 irrespective of the elevation angle of the thick reflecting mirror 101.
Although the above explanation of the prior art concerns a mechanism for supporting a thick reflecting mirror, a support mechanism for a reflecting mirror with a large diameter and support mechanism of a thin reflecting mirror of another prior art will be explained below.
FIGS. 16(a) and 16(b) illustrate reflecting mirrors supporting mechanism disclosed in Japanese Patent Disclosure No. 1-287517, wherein FIG. 16(a) is an oblique view showing an overall structure and FIG. 16(b) is an oblique view showing a structure of a retainer. In the drawing, the numeral 111 denotes a mirror; 112 a mirror cell disposed below the mirror 111; 113 a first supporter for supporting the mirror 111 above the mirror cell 112; 114 a second supporter for supporting the mirror 111 above the mirror cell 112. Although the first supporter 113 and second supporter 114 are comprised of the same components, they differ in installation angle by 90.degree.. The first supporter 113 and second supporter 114 consist of a tube 115, gimbal 116 rotatably connected to tube 115, shaft 117 rotatably connected to the gimbal 116, bearing 118 installed opposite to the gimbal 116 on the shaft 117 and a fixture 119 rotatably connected to the bearing 118. The first supporter 113 is installed in such a manner that the axis of the bearing 118 runs parallel with the x-axis in the drawing, whereas the second supporter 114 is installed in such a manner that the axis of the bearing 118 runs parallel with the y-axis in the drawing.
Next, an operation of the reflecting mirror supporting structure described in FIGS. 16(a) and 16(b) will be explained.
The mirror 111 is supported at three supporting points A, B and C on the mirror cell 112 by the first supporter 113 and two second supporters 114. Displacement of the mirror 111 in the x-direction and z-direction in relation to mirror cell 112 is restricted at supporting point A, whereas displacement in the y-direction and z-direction in relation to the mirror cell 112 is restricted at supporting points B and C. Thus, the mirror 111 is restricted in terms of not only displacement in the x-, y- and z-directions in relation to the mirror cell 112 but also rotation around the x-, y- and z-axes.
Therefore, as is indicated by the arrows in FIG. 16(a), when the mirror cell 112 is deformed in the x-axis direction in relation to the mirror 111, supporting point B or C moves in the x-direction, whereas the mirror 111 moves in x-direction as a rigid body. Furthermore, when the mirror cell 112 is deformed in the y-direction in relation to the mirror 111, supporting point A moves in the y-direction, whereby elastic deformation among the supporting points can be lessened.
One of the prior art thick reflecting mirrors described above has a higher rigidity than its supporting mechanism and thus is not easily deformed, while a thin reflecting mirror is easily deformed.
In the other prior art described above, the shaft 117, bearing 118 and fixture 119 are employed in order to support the mirror in the z- and x-axis directions and in the z- and y-axis directions. Since the bearing 118 is so constructed as to rotate only around the x-axis or y-axis, the gimbal 116 connected to the mirror 111 is able to move only in the y-axis or x-axis direction. Therefore, the mirror 111 is fixed at support point A in the x-axis direction, z-axis direction and around the z-axis, at support point B in the y-axis direction, z-axis direction and around the z-axis and at support point C in the y-axis direction, z-axis direction and around z-axis. In other words, there are nine support directions. Therefore, when a thin reflecting mirror with a low rigidity is employed, deformation of the reflecting mirror supporting mechanism affects the reflecting mirror.
In general, it is possible to prevent an object from moving by deterring displacement in the x-axis, y-axis and z-axis directions and rotation .theta.x around the x-axis, rotation .theta.y around the y-axis and rotation .theta.z around the z-axis. In other words, displacement of an object can be prevented by deterring the above-mentioned six kinds of motion.
When there are nine support directions as in the aforementioned prior art, the results differ depending on whether an object to be supported is a rigid body or not. First, in the case where an object to be supported is a rigid body like a thick reflecting mirror, the mirror will not be deformed even though the reflecting mirror supporting mechanism is deformed. Thus, a reflecting mirror considered as a rigid body like a thick reflecting mirror is not deformed regardless of whether there are more than six support directions or less than six support directions. However, when an object to be supported is a thin reflecting mirror, the mirror is regarded as an elastic body not as a rigid body. Thus, not only the reflecting mirror supporting structure but also the mirror per se will be deformed.
As is clear from the above, in order to support a thin reflecting mirror considered as an elastic body, it is necessary to limit the number of support directions to six.
When supporting a reflecting mirror in six directions (axis directions and rotation directions around the axes), the reflecting mirror can be supported at one point in the center of the mirror in the x, y, z, .theta.x, .theta.y and .theta.z directions (six directions). However, if the reflecting mirror is supported at three points on the periphery of the mirror in such a manner that they are located with as wide a space as possible between respective two points and six directions are fixed at the three points, it is possible not only to prevent deformation of a reflecting mirror but also to increase the characteristic frequency of the reflecting mirror.
The six directions may be fixed by supporting three directions, that is, the R-axis extending in the radial direction of a reflecting mirror, the .theta.-axis extending in the circumferential direction of the reflecting mirror and the Z-axis perpendicular to the surface of the reflecting mirror as well as another three directions, that is, .theta.r around the R-axis, .theta.o around the .theta.-axis and .theta.z around the z-axis.
According to the prior art reflecting mirror support apparatus, when an external force such as wind, etc. acts on the mirror, a rigid body movement, rigid body rotation and local deformation arise on the reflecting mirror. The prior art does not have means for estimating the amount of such movement, rotation or deformation.
Furthermore, if a large force acts on the reflecting mirror as a result of an earthquake, etc., such a force converges on the reflecting mirror support mechanism, which could cause damage to the reflecting mirror.
Still further, it is necessary to make as small as possible the size of a junction between a reflecting mirror and the reflecting mirror support mechanism in order to inhibit the amount of thermal deformation caused by a difference in coefficient of thermal expansion between the reflecting mirror made of heat resistance glass and the reflecting mirror support mechanism, which results in a decline in rigidity of the reflecting mirror support mechanism.
The present invention has been accomplished in order to obviate the aforementioned problems.